The present invention relates to solid state imaging devices and methods for selectively producing normal and mirror image signals.
Video telephones serve to reproduce images of another with whom one is speaking by telephone, and in some cases, provide the ability to produce an image of oneself on the receiving monitor.
The image signal to be transmitted to the distant party is produced as a normal image signal by a television camera of the video telephone. The image of oneself, however, would appropriately be produced as a mirror image, and a normal image signal is not easily employed for this purpose.
Consequently, solid state image pickup devices have been provided with the capability of producing either a normal image signal or a mirror image signal. That is, with the use of such a device, a normal image signal can be transmitted to the other party at a distance, while the mirror image signal may be reproduced by a monitor to provide an image of oneself.
Solid state imaging devices include charge coupled devices (CCD's) having a plurality of picture elements each of which accumulates an electric charge representing an image. The accumulated charge is transmitted as is horizontally and vertically with respect to the device and ultimately converted into an electric image signal which is output by the device. Amplification-type solid state imaging devices, such as MOS-type and JFET-type devices, accumulate charge to develop an image which is read from each of a plurality of picture elements via a respective vertical signal line to a horizontal signal line to be output as an electric image signal.
A conventional amplification-type solid state image pickup device capable of producing either a normal image signal or a mirror image signal is illustrated in FIG. 1 hereof. With respect to FIG. 1, the device includes an image sensor portion 61 coupled with output switches 65 both at an upper horizontal side thereof as well as at a lower horizontal side thereof. The gates of the switches 65 at the upper horizontal side are each coupled with a respective output of an upper horizontal shift register 62 which serves, for example, to control output of a mirror image signal from the device by scanning the upper switches 65 in a first horizontal direction. The .gates of the switches 65 at the lower horizontal side are each coupled with a respective output of a horizontal shift register 63 which serves to control output of a normal image signal from the device by scanning the lower switches 65 in a second horizontal direction opposite the first direction.
The device of FIG. 1 suffers the disadvantage that two horizontal shift registers and two sets of output switches are required, thereby adding a complexity to the device which is not present in imaging devices which produce only a normal image signal and, thus, require only a single horizontal shift register and associated switches. Where both the image sensor portion as well as the shift registers and switches are fabricated on a single substrate, substrate space occupied by the second shift register and associated switches reduces the space available for the image portion, thus reducing the achievable image resolution.